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The effects of psilocybin from so-called magic mushrooms last for more than a year, and may offer a way to help patients with fatal diseases or addictions, according to US researchers.

The findings, which appear in the Journal of Psychopharmacology, follow on from a previous study, which examined the immediate effects of administering psilocybin.

In 2006, Roland Griffiths of Johns Hopkins University in Baltimore, and colleagues gave psilocybin to 36 volunteers, "Under very defined conditions, with careful preparation".

About a third of the volunteers experienced fear and anxiety after taking the psilocybin, but most later reported having a "mystical" or "spiritual" experience.

A year later, more than half of the participants still said the experience increased their sense of well-being or life satisfaction, the researchers write.

"This is a truly remarkable finding," Griffiths says. "Rarely in psychological research do we see such persistently positive reports from a single event in the laboratory."

The findings may offer a way to help treat extremely anxious and depressed patients, or people with addictions, says Griffiths, whose work was funded by the US National Institute on Drug Abuse.

"This gives credence to the claims that the mystical-type experiences some people have during hallucinogen sessions may help patients suffering from cancer-related anxiety or depression and may serve as a potential treatment for drug dependence," Griffiths said.

Strong effects

While psilocybin is widely outlawed, some countries overlook its use by indigenous people in religious ceremonies.

Strict supervision of its use is the key, the researchers note, warning that it should not be given to people at risk for psychosis or certain other serious mental disorders.

While some of the participants reported strong fear or anxiety for a portion of their day-long psilocybin sessions, Griffiths says it didn't last.

"None reported any lingering harmful effects, and we didn't observe any clinical evidence of harm," he says.

Of the volunteers who took the one-day test of psilocybin, 22 of the 36 had a "complete" mystical experience, based on a detailed questionnaire.

Griffiths said 21 continued to rate highly on this standardised scale 14 months later.

"Even at the 14-month follow-up, 58% of the volunteers rated the experience on the psilocybin session as among the five most personally meaningful experiences of their lives and 67% rated it among the five most spiritually significant experiences of their lives," the researchers say.